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Groups > linux.kernel > #1688893

[PATCH 03/15] kernel: convert user_struct.__count from atomic_t to refcount_t

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refcount_t type and corresponding API should be
used instead of atomic_t when the variable is used as
a reference counter. This allows to avoid accidental
refcounter overflows that might lead to use-after-free
situations.

Suggested-by: Kees Cook <keescook@chromium.org>
Reviewed-by: David Windsor <dwindsor@gmail.com>
Reviewed-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
---
 include/linux/sched/user.h | 5 +++--
 kernel/user.c              | 8 ++++----
 2 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/include/linux/sched/user.h b/include/linux/sched/user.h
index 5d5415e..0a9953d 100644
--- a/include/linux/sched/user.h
+++ b/include/linux/sched/user.h
@@ -3,6 +3,7 @@
 
 #include <linux/uidgid.h>
 #include <linux/atomic.h>
+#include <linux/refcount.h>
 
 struct key;
 
@@ -10,7 +11,7 @@ struct key;
  * Some day this will be a full-fledged user tracking system..
  */
 struct user_struct {
-	atomic_t __count;	/* reference count */
+	refcount_t __count;	/* reference count */
 	atomic_t processes;	/* How many processes does this user have? */
 	atomic_t sigpending;	/* How many pending signals does this user have? */
 #ifdef CONFIG_FANOTIFY
@@ -53,7 +54,7 @@ extern struct user_struct root_user;
 extern struct user_struct * alloc_uid(kuid_t);
 static inline struct user_struct *get_uid(struct user_struct *u)
 {
-	atomic_inc(&u->__count);
+	refcount_inc(&u->__count);
 	return u;
 }
 extern void free_uid(struct user_struct *);
diff --git a/kernel/user.c b/kernel/user.c
index 00281ad..c072348 100644
--- a/kernel/user.c
+++ b/kernel/user.c
@@ -90,7 +90,7 @@ static DEFINE_SPINLOCK(uidhash_lock);
 
 /* root_user.__count is 1, for init task cred */
 struct user_struct root_user = {
-	.__count	= ATOMIC_INIT(1),
+	.__count	= REFCOUNT_INIT(1),
 	.processes	= ATOMIC_INIT(1),
 	.sigpending	= ATOMIC_INIT(0),
 	.locked_shm     = 0,
@@ -116,7 +116,7 @@ static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent)
 
 	hlist_for_each_entry(user, hashent, uidhash_node) {
 		if (uid_eq(user->uid, uid)) {
-			atomic_inc(&user->__count);
+			refcount_inc(&user->__count);
 			return user;
 		}
 	}
@@ -163,7 +163,7 @@ void free_uid(struct user_struct *up)
 		return;
 
 	local_irq_save(flags);
-	if (atomic_dec_and_lock(&up->__count, &uidhash_lock))
+	if (refcount_dec_and_lock(&up->__count, &uidhash_lock))
 		free_user(up, flags);
 	else
 		local_irq_restore(flags);
@@ -184,7 +184,7 @@ struct user_struct *alloc_uid(kuid_t uid)
 			goto out_unlock;
 
 		new->uid = uid;
-		atomic_set(&new->__count, 1);
+		refcount_set(&new->__count, 1);
 
 		/*
 		 * Before adding this, check whether we raced
-- 
2.7.4

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[PATCH 00/15] v3 kernel core pieces refcount conversions Elena Reshetova <elena.reshetova@intel.com> - 2017-07-17 12:50 +0200
  [PATCH 07/15] kernel: convert ring_buffer.refcount from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-07-17 12:50 +0200
  [PATCH 02/15] kernel: convert signal_struct.sigcnt from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-07-17 12:50 +0200
  [PATCH 04/15] kernel: convert task_struct.usage from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-07-17 12:50 +0200
  [PATCH 13/15] sched: convert numa_group.refcount from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-07-17 12:50 +0200
  [PATCH 03/15] kernel: convert user_struct.__count from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-07-17 12:50 +0200
  [PATCH 09/15] kernel: convert uprobe.ref from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-07-17 12:50 +0200
  [PATCH 14/15] kernel: convert futex_pi_state.refcount from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-07-17 12:50 +0200
    Re: [PATCH 14/15] kernel: convert futex_pi_state.refcount from  atomic_t to refcount_t Thomas Gleixner <tglx@linutronix.de> - 2017-07-17 16:30 +0200
      RE: [PATCH 14/15] kernel: convert futex_pi_state.refcount from  atomic_t to refcount_t "Reshetova, Elena" <elena.reshetova@intel.com> - 2017-07-17 19:00 +0200
        RE: [PATCH 14/15] kernel: convert futex_pi_state.refcount from  atomic_t to refcount_t Thomas Gleixner <tglx@linutronix.de> - 2017-07-17 20:00 +0200
          RE: [PATCH 14/15] kernel: convert futex_pi_state.refcount from  atomic_t to refcount_t "Reshetova, Elena" <elena.reshetova@intel.com> - 2017-07-18 11:40 +0200
  [PATCH 15/15] kernel: convert kcov.refcount from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-07-17 12:50 +0200
  [PATCH 10/15] kernel: convert nsproxy.count from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-07-17 12:50 +0200
  [PATCH 11/15] kernel: convert group_info.usage from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-07-17 12:50 +0200
  [PATCH 01/15] kernel: convert sighand_struct.count from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-07-17 12:50 +0200
  [PATCH 05/15] kernel: convert task_struct.stack_refcount from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-07-17 12:50 +0200
  [PATCH 06/15] kernel: convert perf_event_context.refcount from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-07-17 12:50 +0200
  [PATCH 12/15] kernel: convert cred.usage from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-07-17 12:50 +0200

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